A conventional gravity operated flush toilet has several basic components. The china components include a porcelain bowl and a porcelain tank mounted on top of the bowl. The bowl and tank may either be separate pieces or may be molded as a single unitary piece of china. The plumbing components of a conventional gravity operated flush toilet include a fill valve in the tank that is connected to a water supply line, a flush valve mounted in a hole in the bottom wall of the tank that communicates with the bowl, a flapper valve that normally closes the flush valve, and a lever or push button on the outer wall of the tank that is connected with a chain or other mechanical linkage for momentarily lifting of the flapper valve. This allows water stored in the tank to flow rapidly through the flush valve into the bowl to carry waste along with the water through a trap connected to the underside of the bowl and into a waste pipe connected to a sewer line, septic tank or other waste reservoir.
Conventional flush valves for gravity operated toilets are generally cylindrical and provide a round valve seat for the flapper valve. They are secured in a drain hole in the bottom wall of the toilet tank from underneath the bottom wall. Typically a large nut is screwed over a male threaded lower portion of the cylindrical flush valve body, on the underside of the bottom wall of the tank. Extending upwardly from the flush valve body is a cylindrical overflow tube. The purpose of the overflow tube is to ensure that a proper water level is maintained within the toilet tank. Ideally, the inlet of the overflow tube is set at a point where it is slightly above normal water level but below the bottom of the flush lever nut that is located on a vertical wall of the tank for actuation of the flushing cycle.
In the United States, there are two basic markets for toilet flush valves, namely, the original equipment manufacturer (OEM) market and the after-installation market. The former consists of large toilet manufacturers that assemble and sell complete gravity operated flush toilets including flush valves. The latter consists of hardware and plumbing supply stores that sell to plumbers and home owners for repair and replacement in toilets already installed in residences.
Every gravity operated flush toilet has an optimum fill level that ensures that enough water is in the tank for proper flushing without wasting water or risking incomplete waste carry out. For many years, gravity operated flush toilets in the United States had tanks with capacities of three and one-half, five gallons, or more. More recently, the Environmental Protection Agency (EPA) has mandated that low water consumption toilets be installed in all new construction and during all re-models, with a maximum water usage of 1.6 gallons per flush. Both the older high volume gravity operated flush toilets and the newer low volume gravity operated flush toilets come in a wide range of tank configurations with different optimum fill levels. Because of this, installation of after-installation market flush valves, which are manufactured in a pre-determined height to accommodate the deepest tank depth likely to be found, typically requires the installer to hand cut the overflow tube of the flush valve to fit. In the experience of this inventor, it would be unduly expensive to manufacture a variety of different overflow valves, each having an overflow tube of different height, to satisfy the configurations of the various gravity operated flush toilets manufactured in the United States and abroad. It is, therefore, advantageous to provide an after-installation flush valve having an adjustable overflow tube that permits plumbers and do-it-yourself homeowners to install the flush valve and to quickly, easily, and without tools, adjust the height of its overflow tube as necessary.